Erythropoietin (EP) is a primary regulator of erythropoiesis. Accordingly, its possible diagnostic and treatment applications in certain refractory anemias has been postulated. The lack of both raw material for erythropoietin purification and relatively pure EP (greater than 150 units/mg protein) has severely compromised its use in research, diagnosis, and treatment. Furthermore, this situation has been complicated by the lack of an accurate, simple assay for biologically active EP. Accordingly, the long term objectives of this investigation are the development of economical procedures for the generation, assay and purification of erythropoietin. Through the use of sheep along with a novel bleed-plasmapheresis procedure, it is believed that large volumes of EP-rich plasma (2-10 units/ml) can be economically produced. This approach will allow for a low cost supply of plasma for EP assay and purification. The in vitro plasma clot technic for culturing erythroid progenitors will be refined and developed as an erythropoietin bioassay. Purification will initially rely on a simplified partial purification procedure based on nitrocellulose-EP binding affinity and standard purification procedures to yield a pure enough EP antigen to generate highly specific EP-antisera (polyclonal and/or monoclonal) which could in turn be used to efficiently purify erythropoietin.